slight backfire sound

hey there ladies and gents i need your help, i am driving a 2000 GS-R with front air intake and HKS cat back Exhaust and thedirect hits ignition system....when i shift fom first to second i hear a sound similar to a low backfire....and yesterday i think i heard it from third to fourth.. what couldcuse this to happen????? please share yur thoughts :confused: :confused: :frog:

backfires are caused by running too rich. it could be that your aftermarket ignition sucks, and is failing from time to time. also check your timing to make sure its in spec.